Connecting a flexible circuit to other structures

ABSTRACT

One example provides a circuit structure comprising a liquid metal conductive path enclosed in an encapsulant, a polymer circuit support comprising a polymer having a functional species available for a condensation reaction, and a cross-linking agent covalently bonding the encapsulant to the polymer circuit support via the functional species.

BACKGROUND

Flexible electrical interconnects may be used to connect electroniccomponents located in portions of a device that are moveable relative toone another. In such a device, a flexible interconnect may be subject toa large number of flexing cycles over a lifetime of the device, and thusmay be susceptible to damage.

SUMMARY

One example provides a circuit structure comprising a liquid metalconductive path enclosed in an encapsulant, a polymer circuit supportcomprising a polymer having a functional species available for acondensation reaction, and a cross-linking agent covalently bonding theencapsulant to the polymer circuit support via the functional species.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a front view of an example computing system.

FIG. 1B shows a side view of the example computing system of FIG. 1A.

FIG. 1C shows a side view of the example computing system of FIG. 1A ina closed state.

FIG. 2 shows a schematic view of an example stretchable interconnectextending between two electrical components.

FIG. 3 shows a cross-sectional schematic view of an example stretchableinterconnect.

FIG. 4 shows an example process for covalently bonding a stretchableinterconnect to an electrical component.

FIG. 5 shows a flow diagram depicting an example method for connecting astretchable circuit element to another circuit element.

DETAILED DESCRIPTION

Electrical interconnects may be incorporated into a variety of devicesto provide electrical pathways between device components. Someelectronic devices may include joints, hinges, and/or other moveablestructures that connect two parts each having electronic components. Insuch structures, a flexible interconnect may be utilized to bridge thecomponents to allow the components to remain electrically interconnectedas the components are moved relative to one another.

Flexible interconnects are commonly formed from solid metal traces, suchas copper, patterned on a flexible substrate, such as a polyimide film.However, the solid metal traces may fatigue over time after repeatedflexing, which may lead to breakage of the traces, thereby disruptingthe electrical connection between the components. Even solid metaltraces that are able to withstand a high number of flex cycles may faildue to pinch points, strain, twist, and/or other modes of deformation.

To address such problems, circuit elements including liquid metalconductors embedded in elastomeric encapsulant materials may be used toform electrical pathways between the components. Deformation of thecircuit elements may cause changes in impedance (e.g., resistance,capacitance, and inductance) which may be measured, enabling such acircuit to also have sensing capabilities. Some such circuits also mayhave the advantage of being stretchable, which may help to mitigate anymechanical stress on the stretchable circuit during such flexing. Thismay help to resist circuit breakage from repeated flexing and/or othermodes of deformation of the circuit compared to interconnects that useonly solid metal traces, even when repeatedly bent to high angles (e.g.approximately 180 degrees in either direction) or deformed with a highand/or concentrated level of force, as the ability for the liquid metalto flow imparts self-healing characteristics to such an interconnect.

In another example, a stretchable/flexible circuit may comprise aconductive composite formed from elastomeric polymer embedded withconductive particulate material (carbon, silver nanowire, etc.) forminga percolating and conducting network, rather than the use of liquidmetal. The conductive composite may also allow for flexing andstretching.

However, connecting such a flexible circuit element to other circuitelements, such as circuit hoards, may pose challenges. For example, useof a pressure-sensitive adhesive (PSA) may create a relatively weakconnection that is prone to delamination over time. It also may bechallenging to form electrical connections through an elastomericencapsulant between the liquid metal conductor and the circuit element.For example, if pins (e.g. integrated circuit pins) or wires areextended through an encapsulant that encloses the liquid metal, the pinsor wires may serve as a point of weakness, potentially allowing liquidmetal conductor to escape.

Accordingly, examples are disclosed that relate to covalently bondingand electrically connecting a flexible circuit element to anothercircuit element, such as a circuit board. In some examples, the flexiblecircuit element also may be stretchable. The covalent bonds between theflexible circuit element and other circuit element may allow flexing,bending, pulling, etc. of the flexible circuit element to occur whilemaintaining a robust mechanical connection to the other circuit element.While described below in terms of a stretchable circuit element, it willbe understood that the disclosed examples also may be used withnon-stretchable circuit elements (e.g. a circuit element comprising anencapsulating layer formed over a non-stretchable flexible material).

A stretchable circuit comprising an encapsulant may be joined to anothercircuit element comprising a polymer circuit support structure (e.g. apolyimide or other polymer film) that includes one or more functionalspecies, such as hydroxyl, thiol, carbonyl, or other suitable group,available for a condensation reaction with a cross-linking agent. Tomediate the condensation reaction, activation of the functional speciesat bonding surfaces via a plasma or other treatment may be performed.Further, in some examples, electrically conductive paths between theencapsulated liquid metal conductor of the stretchable circuit and theother circuit element may be provided by materials embedded in theencapsulant (e.g., carbon molecules, silver nanowires,magnetically-aligned conductive particles, carbon nano tubes, graphite,graphene flakes, silver particles, or silver flakes). The liquid metalitself may also be able to act as a via to connect to the polymercircuit support structure, given a proper seal at the interface. In sucha case, embedded materials may be dispensed with.

FIGS. 1A-1C show an example computing system 100 that may include astretchable circuit, wherein the device takes the form of a tablethaving a display 102. The computing system is connected to a detachablekeyboard unit 104 via a connector 106. The keyboard unit 104 comprises aflexible interconnect that electrically connects keys 110 and otherelectrical components of the keyboard unit 104 to the computing system100 via the connector 106.

The keyboard unit 104 and the flexible interconnect positioned thereinbend around a bottom corner of the display to a front of the display 102in a first flex region 108 a. As illustrated, the bend in this region isrelatively sharp, conforming closely to the corner of the computingsystem 100. The keyboard unit 104 continues up the front surface of thedisplay, and bends sharply down and away from the front surface of thedisplay in a second flex region 108 b. The bend in this region is alsorelatively sharp. FIG. 1C shows flex region 108 b in a straightenedconfiguration when the computing device 100 and keyboard unit 104 are ina “closed” position, as opposed to an “open” position shown in FIGS.1A-1B. Flex region 108 a also may be straightened in a similar manner,for example, when the keyboard unit 104 is removed from the computingdevice. In other examples, an electronic device that utilizes a flexibleinterconnect may take any other suitable form.

As the keyboard unit potentially may be moved between the “open” and“closed” positions, as well as other possible positions, multiple timesa day for potentially years of use, the flex regions 108 a-b may flex avery large number of cycles during the device lifetime. Thus, the use ofa stretchable interconnect having a liquid metal may help prevent lossof conductivity due to stress-induced damage.

FIG. 2 shows an example stretchable circuit element, in the form ofstretchable interconnect 200 that may be utilized to provide signalpaths in a portion of a device configured to provide a movable orflexible joint, such as the flex regions described above for computingdevice 100. Similar structures may be used as electrical circuitelements in other stretchable environments, such as in clothing,upholstery, medical devices, etc.

The interconnect 200 includes a plurality of conductive pathways 206 anda substrate 208, and extends between a first electrical component 202 inthe form of a connector and a second electrical component 204 in theform of a circuit board having various electronic elements. In otherexamples, components 202 and 204 may take any other suitable form, suchas an integrated circuit. A longitudinal axis 210 is shown forreference.

The conductive pathways 206 comprise a liquid metal conductor supportedby the substrate 208. Liquid metal can flow to fill the shape of achannel that holds the liquid metal, and therefore is not subject to thefatigue and breakage issues of solid metal traces when repeatedly bent.In various examples, the liquid metal may be used in place of a solidconductor, or (where the circuit is flexible but not stretchable) may beused in addition to the solid conductor to provide self-healingcapabilities for a solid metal trace when the solid metal trace breaks.As used herein, liquid metals may be defined as pure metals or metalalloys with a sufficiently low melting point (Tm) to be in a liquidstate at room temperature. Non-limiting examples include eutecticgallium/indium (eGaIn), other gallium/indium alloys, eutecticgallium/indium/tin (Galinstan), and other gallium alloys, Solidconductors may be defined as electrical conductors having a Tm that issufficiently above room temperature (e.g., higher than the Tm of liquidmetals/conductors), such that the solid metal/conductor is solid at roomtemperature and at ordinary device operating temperatures. In otherexamples, the conductive paths may be formed from an elastomeric polymerembedded with conductive particulate material (carbon, silver nanowire,etc.) rather than or in addition to the liquid metal.

The first electrical component 202 and the second electrical component204 include one or interfaces (e.g., contact 212) for coupling to theconductive pathways of the interconnect 200. In order to provide anelectrical path between the electrical components and the conductivepathways 206 of the interconnect, an encapsulant 214 comprisingelectrical paths between the conductive pathways and an exterior surfaceof the interconnect optionally may be formed over at least a portion ofthe liquid metal conductive pathways 206. In various examples, theelectrical paths may comprise magnetically aligned conductive particles,silver nanowires, and/or composite material (e.g., carbon moleculesmixed with the polymer of the encapsulant). In the illustrated example,the encapsulant 214 is positioned at terminal regions of the conductivepathways, such that a middle region of the conductive pathways is notencapsulated by the encapsulant 214 with electrical paths, but insteadby an encapsulant 216 without such paths. In other examples, theencapsulant 214 comprising the electrical paths may be formed over thefull length of the conductive pathways.

In various instances, such as with aligned magnetic particles, theelectrical paths between the conductive pathways and the exteriorsurface may be anisotropically conductive, in that they conductelectricity along a direction of the particle alignment but not in otherdirections. Such structures may allow electrical connections to beformed between different interconnect lines and corresponding circuitelement connectors without having to pattern the encapsulant material.In other examples that do not use an anisotropic conductive material,the conductive portions of the encapsulant may be patterned to avoidforming undesired electrical connections.

FIG. 3 shows a sectional view of a portion of stretchable interconnect200 of FIG. 2. The substrate 208 may be formed at least partially fromany suitable electrically insulating, flexible material, such assilicone polymers. In other examples, the substrate may be formed from aflexible, but not stretchable, material. In the depicted example, theliquid metal conductor 206 is in contact with the substrate 208. Inexamples where a non-stretchable substrate is used, a solid metalconductive trace layer may be located between the liquid metal conductor206 and the substrate 208.

Any suitable liquid metal may be used as liquid metal conductor 206,including the liquid metal materials described above. The liquid metal206 may be deposited in any desired manner. For example, an alloy ofgallium may be deposited via a needle orifice or the like directly ontothe substrate. The outer surface of such an alloy, when exposed to air,forms a thin oxide layer that prevents the liquid metal from spreading,and thus retains the shape in which the liquid metal is initiallydeposited. In other examples, the encapsulating layer 216 may first beapplied over the substrate 208, then a channel formed between thesubstrate 208 and the encapsulating layer 216, and then the liquid metalintroduced into the channel (e.g. by injection or pressuredifferentials). Other example methods of depositing the liquid metalinclude electrochemically depositing the liquid metal from a bath, orspreading the liquid metal onto the solid metal trace, where selectivewetting between the liquid metal and the substrate may constrain theshape of the liquid metal.

The encapsulating layer 216 helps to retain the liquid metal layer in adesired location, and electrically insulates the conductive pathways. Insome examples, the encapsulating layer 216 may be formed at leastpartially from a siloxane-based polymer. For example, the siloxane-basedpolymer may comprise a siloxane-based polymer, such as silicon rubber,or the siloxane-based polymer may include an elastomer, such aspolyurethane or polyacrylic, with silicon-based fillers such as silica.The encapsulating layer 216 contacts the substrate 208 in regionsbetween conductive pathways 206. The encapsulating layer 216 may bedeposited in any suitable manner, depending upon the polymer used. Forexample, a silicone polymer may be deposited in a fluid state, and thenhardened. Where the encapsulating layer is added prior to liquid metalinclusion, a channel may be formed at the interface of the substrate andthe encapsulating layer after formation of the encapsulating layer, andthe liquid metal then may be added to the channel. In other examples,materials other than siloxane-based polymers may be used.

In the example shown in FIG. 3, the encapsulant 214 in the terminalregions includes electrically conductive particles that are magneticallyaligned to exhibit anisotropic conductivity. The conductivelyanisotropic, magnetic particle-embedded encapsulant 214 is formed from asiloxane-based polymer (e.g. a silicone polymer) 302 that is embeddedwith magnetic particles 304. The particles are first aligned via amagnetic field, and then the siloxane-based polymer his hardened to trapthe particles in the aligned state. The magnetic particles 304 mayinclude a core of ferromagnetic material (e.g. nickel or iron) orparamagnetic material coated with an electrical conductor copper, gold,silver, and/or other conductive material(s)). In other examples, theencapsulant 214 may comprise silver nanowires, and/or a conductor suchas carbon black.

The flexible and/or stretchable circuit structure formed by liquid metalconductive pathways 206, encapsulant 216, and electrical path-containingterminal encapsulant 214 is coupled to one or more circuit elements whenused in a device. Examples of such circuit elements are illustrated inFIG. 2 as first electrical component 202 and the second electricalcomponent 204. During device use, the coupling between the stretchablecircuit structure and electrical components may be flexed, bent,twisted, compressed, stretched, etc. Over time, the coupling(s) betweenthe stretchable circuit structure and other circuit structure(s) may beprone to degradation. Thus, in order to form a robust mechanicalconnection and reliable electrical connection between the stretchablecircuit structure and the other electrical components, acovalently-bonded interface 306 between the electrical components andthe stretchable circuit structure is formed. The interface 306 comprisesa cross-linking agent bonded both to the siloxane-based encapsulant ofthe stretchable circuit structure and a polymer surface of the othercircuit element (e.g., the polymer substrate of the circuit board) thatforms covalent bonds to each of these structures.

FIG. 4 shows an example process 400 for covalently bonding asiloxane-containing circuit structure to another circuit structure.Process 400 may be carried out, for example, to bond the stretchablecircuit structure of FIGS. 2 and 3 to one or more other electricalcomponents, such as the first electrical component 202 and secondelectrical component 204. In the depicted example, process 400 involvesbonding of a polymer circuit support to a siloxane-containingencapsulant of a stretchable circuit structure via a cross-linkingmolecule that includes a siloxane functional group and an aminefunctional group; however, other functional groups may be used in otherimplementations. Likewise, in other examples, a non-stretchable circuit(e.g. a flexible circuit) structure comprising a siloxane outer surface,such as a polyimide circuit comprising a solid metal/liquid metal tracecovered by a siloxane-based encapsulant may be bonded to other circuitstructure following method 400.

At 402, process 400 comprises activating a surface of a polymer circuitsupport 401 of an electrical component to which the stretchable circuitstructure is to be bonded. The polymer circuit support 401 may compriseany suitable polymer material, including a polyimide, polycarbonate,polyethylene terephthalate, and/or polyvinyl chloride. In some examples,the polymer circuit support may comprise a core material (e.g. a fibermaterial, such as fiber board) coated with another polymer material,such as one or more of those listed above. Activating the surface of thepolymer circuit support 401 may include exposing the polymer circuitsupport 401 to a plasma, such as an oxygen plasma, air plasma, or argonplasma. Other types of activation also may be used, such as exposing thepolymer circuit support to a corona discharge.

At 404, a layer of a cross-linking agent is applied to the activatedsurface of the polymer circuit support 401. In one example, thecross-linking agent may comprisepoly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane] (PDMS-amine). Inother examples, other cross-linking agents that include a siloxanefunctional group and an amine functional group may be used, such ascross-linking agents that include a different side group (e.g., anotheralkyl group, such as polydimethylsiloxane, or an aryl group such aspolydimethylsiloxane). Further, some examples may utilize cross-linkingagents having a non-amine functional group for bonding to the polymercircuit element, such as a carboxyl, benzo phenol, sulfide, or phosphidegroup. When the cross-linking agent is applied, the activated surface ofthe polymer circuit support forms a covalent linkage, in this example aurethane bond, with the amine functional group of the cross-linkingagent.

At 406, the cross-linking agent covalently bonded to the polymer circuitsupport 401 is activated via the plasma treatment (e.g., oxygen, air,and/or argon plasma), exposure to corona discharge, or other suitablemechanism to oxidize the siloxane-containing functional group of thecross-linking agent. Likewise, at 408, a stretchable circuit structure403 is activated via plasma, corona, or other suitable treatment. Insome examples, the stretchable circuit structure comprises asiloxane-based encapsulant. Examples of suitable siloxane-basedmaterials include, but are not limited to, polymethyl vinylsiloxane,polymethylphenylsiloxane, polyhydrogenmethylsiloxane, andpolysilsesquioxanes.

At 410, the activated stretchable circuit structure is bonded to theactivated cross-linking agent on the polymer circuit support 401. Thebonding may include pressing or otherwise bringing the activatedsurfaces into contact, and also may involve a thermal treatment (e.g.,heating the structure for a suitable duration of time, such as for anhour). As a result, a covalent linkage (in this example, a siloxaneSi—O—Si bond) is formed between the cross-linking agent and the siloxaneencapsulant.

In examples where the encapsulant of the stretchable circuit structuredoes not include silicone (e.g., a polyurethane or polyacrylicelastomer), the cross-linker may be applied to both the circuit supportsurface and the encapsulant surface and the siloxane covalent bond mayoccur between the functional groups of the cross-linking agent.

FIG. 5 shows a flow chart illustrating an example method 500 forcovalently bonding a circuit element having a siloxane-basedencapsulant, such as a stretchable siloxane-based circuit structure, toanother circuit element comprising a polymer circuit support. Asdescribed above, the circuit element may comprise electricallyconductive paths between a liquid metal conductor in the circuitstructure and an exterior of the siloxane-based encapsulant to formconnections to the other circuit elements.

At 502, method 500 includes activating a surface of the polymer circuitsupport. The polymer circuit support may take the form of a substrate,such as a printed circuit board, that supports various circuit elements.The polymer circuit support may be formed from any suitable material,including polyimide, polycarbonate, polyethylene terephthalate,polyvinyl chloride, or other suitable polymer material. The activationmay include application of a plasma, corona discharge, or other suitabletreatment.

At 504, a cross-linking agent s applied to the activated surface of thepolymer circuit support. The cross-linking agent may include a firstfunctional group comprising a siloxane moiety such aspolydimethylsiloxane, polydimethylsiloxane, and/or polydimethylsiloxane,and a second functional group configured to create a linkage with theactivated surface of the polymer circuit support, such as an amine,sulfide, or phosphide group. In one example, the cross-linking agentincludes poly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane], alsoreferred to as PDMS-amine. The application of the cross-linking agent tothe polymer circuit support results in the formation of a covalent bondbetween the amine functional group and the polymer circuit support.

At 506, a surface of the siloxane-based encapsulant of the stretchablecircuit structure is activated along with the siloxane functional groupof the cross-linking agent (now bonded to the polymer circuit support)via exposure to a plasma, corona discharge, and/or any other suitabletreatment.

At 508, the activated siloxane-based encapsulant is bonded to thepolymer circuit support, thereby covalently bonding the stretchablecircuit element to the polymer circuit support. As indicated at 510,this may include forming a siloxane bond between the activated siloxaneof the encapsulant and the activated siloxane functional group of thecross-linking agent. This process also may cause, at 512, formation ofan electrical coupling between a circuit element of the polymer circuitsupport and the liquid metal conductor via the electrical path withinthe encapsulant. For example, when the activated siloxane-basedencapsulant is brought into contact with circuit elements on the polymercircuit support during the bonding process, the previously describedelectrical path(s) within the encapsulant (such as nanowires,magnetically aligned particles, etc.) may contact corresponding circuitelement(s) on the polymer circuit support to form the electricalcoupling. In other examples, a conductor may be inserted through theencapsulant to reach the liquid metal material, and then the interfacebetween the conductor and the encapsulant may be sealed.

Another example provides a device comprising a circuit structurecomprising a conductive path enclosed in a siloxane-based encapsulant, apolymer circuit support, and a cross-linking agent covalently bondingthe siloxane-based encapsulant to the polymer circuit support, thecross-linking agent comprising a siloxane functional group covalentlylinked to the siloxane-based encapsulant and a second functional groupcovalently linked to the siloxane functional group and the polymercircuit support. The conductive path may additionally or alternativelycomprise one or more of liquid metal and a polymer embedded withconductive particulate material, the siloxane functional group mayadditionally or alternatively comprise one or more ofpolydimethylsiloxane, polydimethylsiloxane, and polydimethylsiloxane,and the second functional group may additionally or alternativelycomprise one or more of an amine, a sulfide, and a phosphide. Thepolymer circuit support may additionally or alternatively comprise oneor more of polycarbonate, polyethylene terephthalate, polyvinylchloride, and polyimide. The device may additionally or alternativelycomprise an electrical coupling between the conductive path of thecircuit structure and a circuit element on the polymer circuit support.The electrical coupling may additionally or alternatively comprisealigned magnetic particles embedded in the siloxane-based encapsulant.The electrical coupling may additionally or alternatively comprise oneor more of silver nanowires, silver particles, and silver flakes. Theelectrical coupling may additionally or alternatively comprise carbonmolecules embedded in the siloxane-based encapsulant. Any or all of theabove-described examples may be combined in any suitable manner invarious implementations.

Another example provides a method of manufacturing a device comprisingencapsulating a liquid metal conductor in a siloxane-based encapsulantto form a conductive path of a flexible circuit structure, activating asurface of a polymer circuit support, applying a cross-linking agent tothe surface of the polymer circuit support after activating the surface,the cross-linking agent comprising a siloxane functional group and asecond functional group bound to the siloxane functional group, thesecond functional group covalently bonding to the activated surface ofthe polymer circuit support, activating the siloxane functional group ofthe cross-linking agent, and covalently bonding the siloxane-basedencapsulant to the activated siloxane functional group of thecross-linking agent. Activating the surface of the polymer circuitsupport may additionally or alternatively comprise exposing the surfaceof the polymer circuit support to one or more of an oxygen plasma, anair plasma, and an argon plasma, and activating the siloxane functionalgroup of the cross-linking agent additionally or alternatively comprisesexposing the siloxane functional group of the cross-linking agent to oneor more of oxygen plasma, air plasma, and argon plasma. The method mayadditionally or alternatively comprise prior to bonding thesiloxane-based encapsulant to the activated siloxane functional group ofthe cross-linking agent, activating the siloxane-based encapsulant byexposing the siloxane-based encapsulant to one or more of an oxygenplasma, an air plasma, and an argon plasma. The method may additionallyor alternatively comprise forming an electrical coupling between theliquid metal conductor of the flexible circuit structure and a circuitelement of the polymer circuit support. The method may additionally oralternatively comprise at least a portion of the siloxane-basedencapsulant including embedded magnetic particles. The method mayadditionally or alternatively comprise at least a portion of thesiloxane-based encapsulant comprising embedded nanowires. Activating thesurface of the polymer circuit support may additionally or alternativelycomprise activating a surface of a polycarbonate, a polyethyleneterephthalate, a polyvinyl chloride, or a polyimide circuit support.Applying the cross-linking agent to the surface of the polymer circuitsupport may additionally or alternatively comprise applyingpoly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane]. Any or all ofthe above-described examples may be combined in any suitable manner invarious implementations.

Another example provides for a device comprising a first circuit elementon a first polymer circuit support, a second circuit element on a secondpolymer circuit support, an interconnect between the first circuitelement acid the second circuit element, the interconnect comprising, aliquid conductive pathway encapsulated in a siloxane-based encapsulant,and an electrical path that interfaces with the liquid conductivepathway between the liquid conductive pathway and one or more of thefirst circuit element and the second circuit element, the electricalpath extending through the siloxane-based encapsulant,and across-linking agent covalently bonding the siloxane-based encapsulant tothe first circuit support and the second circuit support, thecross-linking agent comprising a siloxane functional group bound to thesiloxane-based encapsulant and a second functional group bound to thesiloxane functional group and the first polymer circuit support andsecond polymer circuit support. The siloxane functional group mayadditionally or alternatively comprise one or more ofpolydimethylsiloxane, polydimethylsiloxane, and polydimethylsiloxane.The second function group may additionally or alternatively comprise oneor more of an amine, a carboxyl, a benzo phenol, a sulfide, and aphosphide. The first polymer circuit support and second polymer circuitsupport each may additionally or alternatively comprise one or more ofpolycarbonate, polyethylene terephthalate, polyvinyl chloride, andpolyimide. The electrical path may additionally or alternativelycomprise one or more of aligned magnetic particles, silver nanowires,carbon nano tubes, graphite, graphene flakes, silver particles, silverflakes, and carbon molecules embedded in the siloxane-based encapsulant.Any or all of the above-described examples may be combined in anysuitable manner in various implementations.

It will be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing straegetes. As such, various acts illustrated and/ordescribed may be performed in the sequence illustrated and/or described,in other sequences, in parallel, or omitted. Likewise, the order of theabove-described processes may be changed.

The subject matter of the present disclosure includes all novel andnon-obvious combinations and sub-combinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

1. A device, comprising: a circuit structure comprising a conductivepath enclosed in an encapsulant; a polymer circuit support comprising apolymer having a functional species available for a condensationreaction; and a cross-linking agent covalently bonding the encapsulantto the polymer circuit support via the functional species.
 2. The deviceof claim 1, wherein the encapsulant is a siloxane-based encapsulant, andwherein the cross-linking agent comprises a siloxane functional groupcovalently linked to the siloxane-based encapsulant and a secondfunctional group covalently linked to the siloxane functional group andthe functional species of the polymer circuit support.
 3. The device ofclaim 2, wherein the conductive path comprises one or more of liquidmetal and a polymer embedded with conductive particulate material,wherein the siloxane functional group comprises one or more ofpolydimethylsiloxane, polydimethylsiloxane, and polydimethylsiloxane,wherein the second functional group comprises one or more of an amine, asulfide, and a phosphide, and wherein the polymer circuit supportcomprises one or more of polycarbonate, polyethylene terephthalate,polyvinyl chloride, and polyimide.
 4. The device of claim 1, furthercomprising an electrical coupling between the conductive path of thecircuit structure and a circuit element on the polymer circuit support.5. The device of claim 4, wherein the electrical coupling comprisesaligned magnetic particles embedded in the encapsulant.
 6. The device ofclaim 4, wherein the electrical coupling comprises one or more of silvernanowires, silver particles, and silver flakes embedded in theencapsulant.
 7. The device of claim 4, wherein the electrical couplingcomprises carbon molecules embedded in the encapsulant.
 8. A method ofmanufacturing a device, the method comprising: encapsulating a liquidmetal conductor in a siloxane-based encapsulant to form a conductivepath of a flexible circuit structure; activating a surface of a polymercircuit support; applying a cross-linking agent to the surface of thepolymer circuit support after activating the surface, the cross-linkingagent comprising a siloxane functional group and a second functionalgroup bound to the siloxane functional group, the second functionalgroup covalently bonding to the activated surface of the polymer circuitsupport; activating the siloxane functional group of the cross-linkingagent; and covalently bonding the siloxane-based encapsulant to theactivated siloxane functional group of the cross-linking agent.
 9. Themethod of claim 8, wherein activating the surface of the polymer circuitsupport comprises exposing the surface of the polymer circuit support toone or more of an oxygen plasma, an air plasma, and an argon plasma, andwherein activating the siloxane functional group of the cross-linkingagent comprises exposing the siloxane functional group of thecross-linking agent to one or more of oxygen plasma, air plasma, andargon plasma.
 10. The method of claim 8, further comprising, prior tobonding the siloxane-based encapsulant to the activated siloxanefunctional group of the cross-linking agent, activating thesiloxane-based encapsulant by exposing the siloxane-based encapsulant toone or more of an oxygen plasma, an air plasma, and an argon plasma. 11.The method of claim 8, further comprising forming an electrical couplingbetween the liquid metal conductor of the flexible circuit structure anda circuit element of the polymer circuit support.
 12. The method ofclaim 11, wherein at least a portion of the siloxane-based encapsulantincludes embedded magnetic particles.
 13. The method of claim 11,wherein at least a portion of the siloxane-based encapsulant comprisesembedded nanowires.
 14. The method of claim 8, wherein activating thesurface of the polymer circuit support comprises activating a surface ofa polycarbonate, a polyethylene terephthalate a polyvinyl chloride, or apolyimide circuit support.
 15. The method of claim 8, wherein applyingthe cross-linking agent to the surface of the polymer circuit supportcomprises applyingpoly[dimethylsiloxane-co-(3-aminopropyl)methylsiloxane].
 16. A devicecomprising: a first circuit element on a first polymer circuit support;a second circuit element on a second polymer circuit support; aninterconnect between the first circuit element and the second circuitelement, the interconnect comprising a liquid conductive pathwayencapsulated in a siloxane-based encapsulant, and an electrical paththat interfaces with the liquid conductive pathway between the liquidconductive pathway and one or more of the first circuit element and thesecond circuit element, the electrical path extending through thesiloxane-based encapsulant; and a cross-linking agent covalently bondingthe siloxane-based encapsulant to the first circuit support and thesecond circuit support, the cross-linking agent comprising a siloxanefunctional group bound to the siloxane-based encapsulant and a secondfunctional group bound to the siloxane functional group and the firstpolymer circuit support and second polymer circuit support.
 17. Thedevice of claim 16, wherein the siloxane functional group comprises oneor more of polydimethylsiloxane, polydimethylsiloxane, andpolydimethylsiloxane.
 18. The device of claim 16, wherein the secondfunction group comprises one or more of an amine, a carboxyl, a benzophenol, a sulfide, and a phosphide.
 19. The device of claim 16, whereinthe first polymer circuit support and second polymer circuit supporteach comprise one or more of polycarbonate, polyethylene terephthalate,polyvinyl chloride, and polyimide.
 20. The device of claim 16, whereinthe electrical path comprises one or more of aligned magnetic particles,silver nanowires, carbon o tubes, graphite, graphene flakes, silverparticles, silver flakes, and carbon molecules embedded in thesiloxane-based encapsulant.